Hydrogen storing member and process for storing hydrogen into the hydrogen storing member

ABSTRACT

A hydrogen storing member which comprises at least two kinds of hydrogen storing materials comprising a first hydrogen storing material and a second hydrogen storing material capable of releasing or storing hydrogen in a range of at least one of temperature and pressure at which the first hydrogen storing material is in the β phase having a high capacity for storing hydrogen.

This application is a division of application Ser. No. 08/345,714, filedNov. 22, 1994, now U.S. Pat. No. 5,567,303, which, in turn, is adivision of application Ser. No. 08/034,648 filed Mar. 22, 1993, nowissued as U.S. Pat. No. 5,391,366, issued Feb. 21, 1995, which is acontinuation of application Ser. No. 07/562,904, filed Aug. 6, 1990, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a hydrogen storing member capable of storinghydrogen and a process for storing hydrogen into the hydrogen storingmember, and particularly to a hydrogen storing member capable of storinghydrogen at a high concentration without scaling-up of an apparatus forstoring hydrogen and a process for storing hydrogen into the hydrogenstoring member. Thus, the present invention relates to a hydrogenstoring member widely applicable to an apparatus for hydrogenpurification and recovery, a heat pump, an apparatus for storinghydrogen, an actuator, an apparatus for cold nuclear fusion, etc. and aprocess for storing hydrogen into the hydrogen storing member.

2. Related Background Art

Recently, hydrogen has been attracting attention as an energy source inplace of the fossil fuel. The attractive points of hydrogen areparticularly that water is a raw material and thus hydrogen as aresource has no limit; hydrogen causes no environmental pollutions; arehydrogen has a wide field of applications; hydrogen can serve as a meansfor storing other energy; and hydrogen can be used for energytransportation. Now, the transportation and storage of hydrogen arecarried out in the form of a compressed hydrogen gas or liquefiedhydrogen, which is not always regarded as an efficient process fortransporting or storing hydrogen from the viewpoints of safety,transportation-storage efficiency and economy.

Recently, hydrogen storing materials are attracting attentions as aprocess for storing hydrogen, because hydrogen can be stored at adensity equal to or higher than that of liquefied hydrogen.

As the process for storing hydrogen into a hydrogen storing membercomposed of a hydrogen storing alloy (metal), the following two mainprocesses have been so far available. The first process is to bringabout a vessel containing a hydrogen storing member into a hydrogen(light hydrogen) gas atmosphere compressed to a few to a few tens ofatmospheres and to utilize a solid solution equilibrium of a metalhydride composed of two elements, i.e. a metal and hydrogen under a highpressure, thereby conducting hydrogen storage. The second process is touse a hydrogen storing alloy as a cathode and storing hydrogen (lighthydrogen) generated at the cathode by electric current passage into thehydrogen storing alloy as an application of water electrolysis.

Usually, the hydrogen content in the hydrogen storing material accordingto the first process depends upon the hydrogen gas pressure in thevessel and the temperature of the hydrogen storing alloy, and thehydrogen content abruptly increases with higher pressure of the hydrogengas or lower temperature of the hydrogen storing material. When a metalor an alloy is used as a hydrogen storing material in this manner,hydrogen storage is carried out by utilizing the phenomenon that thestructure of the hydrogen storing material depends upon the temperatureor the pressure and thus the quantity of stored hydrogen is also changedthereby.

In the second electrolysis process, the pressure on the cathode surfacedepends upon the applied voltage at the electrolysis and thus thepressure on the cathode surface can be increased from a few atmospheresto a few tens of atmospheres by increasing the voltage.

On the other hand, very recently, nuclear fusion using a hydrogenstoring member has been reported and the usefulness of the hydrogenstoring member in the nuclear fusion has been pointed. That is, in theso far proposed nuclear fusion processes, a high temperature plasma ofdeuterium is maintained by the action of magnetic field, or compressedto a high density, and the nuclear fusion reaction is carried out beforethe scattering of the plasma. Thus, in order to maintain the hightemperature plasma in a confined state for a long time, a very largeapparatus based on the Tokamak system has been used. On the other hand,it has been recently reported that cold nuclear fusion can be generatedaccording to a simple process for electrolysing a heavy water solutioncontaining many kinds of metal ions, using a hydrogen storing membercomposed of a simple metal such as Pd, Ti, etc. as a cathode. The coldnuclear fusion is carried out by combining deuterium in a hydride of Pdor Ti by electrolysis, using a simple metal of Pd or Ti capable ofdeuterium as a cathode. For example, S. E. Jones et al reported inNature 338 (1989) 737 "observation of cold nuclear fusion in condensedmatter" that neutrons generated during the electrolysis were measured bya high sensitive detector and neutrons of 2.5 MeV were detected thereby,and proved that the nuclear fusion reaction took place to a very slightdegree. Thus, the hydrogen storing member and a process for storinghydrogen are attracting attentions in the nuclear fusion.

However, the process requiring a high pressure or a low temperature instoring hydrogen into the hydrogen storing member has such problems asscale-up of the apparatus for carrying out the process, an increase inthe operating cost and a difficulty to control the atmosphere in whichthe hydrogen storing member is placed (control of pressure, etc.).

On the other hand, particularly in case of applying the hydrogen storingmember to the nuclear fusion, thereby occasioning the nuclear fusionreaction efficiently, deuterium must be stored in excess in the hydrogenstoring member. In the conventional process it was impossible to storethe deuterium in much excess in the hydrogen storing member. For thisreason, the probability of nuclear fusion reaction was low and theabsolute amount of detected neutrons was very small.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-mentionedproblems and provide a hydrogen storing member capable of efficientlystoring hydrogen at a high concentration and a process for storinghydrogen in the hydrogen storing member.

Another object of the present invention is to provide a hydrogen storingmember capable of efficiently storing hydrogen at a high concentrationwithout scale-up of an apparatus for storing hydrogen into the hydrogenstoring member or an increase in the operating cost or without thedifficulty to control the atmosphere in which the hydrogen storingmember is placed, and also to provide a process for storing hydrogen inthe hydrogen storing member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one structure of ahydrogen storing member according to the present invention.

FIGS. 2 and 3 are diagrams showing isotherms between the pressure andthe composition in systems of hydrogen storing member and deuterium.

FIG. 4 is a schematic view showing an apparatus for storing hydrogen ina solution, applicable to the present invention.

FIG. 5 is a schematic view showing an apparatus for storing hydrogenunder pressure in a gas atmosphere applicable to the present invention.

FIG. 6 is a schematic cross-sectional view of another structure of ahydrogen storing member according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention utilizes the phenomena that the hydrogen storingcapacity of a hydrogen storing material is greatly changed by suchexternal factors as temperature, pressure, etc. and the temperature andpressure at which the change takes place depend upon the species of thehydrogen materials. That is, when for example, two kinds of hydrogenstoring materials are used, hydrogen is stored into the first hydrogenstoring material and the second hydrogen storing material at such a lowtemperature that these two hydrogen storing materials can store muchhydrogen, and then hydrogen is released from the second hydrogen storingmaterial at such a high temperature that hydrogen is released only fromthe second hydrogen storing material, thereby forcely making thereleased hydrogen intrude into the adjacent first hydrogen storingmaterial. That is, hydrogen can be efficiently stored in excess into thefirst hydrogen storing material.

More detailed explanation of the hydrogen storing function will be madebelow, referring the case of using two different kinds of the first andsecond hydrogen storing materials. The term "hydrogen" herein used meanslight hydrogen, deuterium, tritium or their mixture, unless otherwisespecifically mentioned.

FIG. 2 is a diagram showing isothermal curves of pressure-composition ofPd--D system as one example of hydrogen storing material-deuterium (D).

In FIG. 2 the region shown by 1 is a region of single α phase having asmall hydrogen storing capacity, the region shown by 2 is a region ofsingle β phase having a large hydrogen storing capacity and the regionshown by 3 is a two-phase coexisting region of α+β phases. For example,under a deuterium pressure 1 to 10 atm and at a temperature of 5° to 50°C., Pd metal is a simple metal of β phase.

FIG. 3 is a diagram showing isothermal curves of pressure-composition ofalloy as deuterium storing materials suitable for the present invention.Under a deuterium pressure of 1 atm, the deuterium storing alloy is inthe β phase at 5° C., and in the α phase 30° C. or higher. That is thedeuterium is stored in the β phase deuterium storing alloy at 5° C. andthen the β phase is shifted to the α phase by elevating the temperatureto 30° C. or higher to release the stored deuterium from the deuteriumstoring alloy.

That is, in this embodiment a hydrogen storing member is constitutedfrom a first deuterium storing material and a second deuterium storingmaterial (alloy) capable of phase shifting between the α phase and the βphase (α←→β) within temperature and pressure range in which the firstdeuterium storing material is kept in the β phase, and heavy water issupplied to the hydrogen storing member from the outside. By subjectingthe hydrogen storing member to an appropriate temperature cycle, storingor release of deuterium in or from the second hydrogen storing materialis carried out and pumping of deuterium into the first deuterium storingmaterial provided on the inner side is carried out to increase thehydrogen concentration in the first deuterium storing material.

In the foregoing embodiment, two kinds of hydrogen storing materialshaving different transition points for hydrogen storage and release areused, but it is needless to say that a combination of more than twokinds of hydrogen storing materials can be used, so long as they havedifferent transition points for hydrogen storage and release.

Furthermore, in the foregoing embodiment the transition (phase shifting)for hydrogen storage and release is occasioned by changing thetemperature, but as is evident from FIGS. 2 and 3, the transition can beoccasioned by changing the pressure or by changing both temperature andpressure. The transition by changing the temperature or the pressure canbe occasioned not only once, but also repeatedly, for example, severaltimes.

Any combination of materials can be used in the present invention forthe hydrogen storing member, so long as the materials have theabove-mentioned characteristics. The hydrogen storing materials for usein the present invention include, for example, simple metals such as Pd,Ca, Mg, Ti, Zr, V, Nb, Fe, etc. and alloys containing at least one ofthese simple metals. The hydrogen storing alloys for use in the presentinvention include, for example, Pd-based alloys, Mg-based alloys such asMg₂ Cu, Mg₂ Ni, etc., Ti-based alloys such as TiFe, TiCo, TiMn, TiCr₂,etc., and Zr-based alloys such as ZrMn₂, etc. Rare earth element-basedalloys containing at least one of rare earth elements represented by Laor Mm (misch metal), etc. can be used, and also La--Ni-based alloys suchas LaNi₅, etc., Mm--Ni-based alloys such as CaMmNiAl, etc. can be used.Among these hydrogen-storing metals and alloys, it is particularlydesirable to form the hydrogen storing member from combinations ofPd/LaNi₅, Pd/FeTi, Ti/LaNi₅, etc.

The structure of the hydrogen storing member can be such a layerstructure that one hydrogen storing material encloses another hydrogenstoring material. The layer structure must be a structure of a pluralitylayer, which can be constituted by different kinds of hydrogen storingmaterials or can be constituted by repetitions of several kinds ofhydrogen storing material layers.

Furthermore, the hydrogen storing member can be in such a structure thatparticles of one hydrogen storing material are distributed in a matrixformed from another hydrogen storing material. When it is taken intoconsideration that all the hydrogen released from the second hydrogenstoring material is absorbed into the first storing material, therebystoring the hydrogen in the first hydrogen storing material at a highdensity, it is desirable that the hydrogen storing member is in such astructure that the second hydrogen storing material may not be exposedto the surrounding atmosphere to the utmost or at all. In order toincrease the probability of occasioning cold nuclear fusion, it isdesirable that the first hydrogen storing material is in an expandedstate to some extent and thus the first hydrogen storing material as abulky matrix is covered with the second hydrogen storing material, whichis further covered with the first hydrogen storing material. However,the hydrogen storing member is not always constituted by the hydrogenstoring material in a bulky state, that is, parts or the entirety of thehydrogen storing member may be constituted by a powdery hydrogen storingmaterial.

The shape of the hydrogen storing member is not limited to a sheet form,a plate form, a spherical form, a rod form, etc. and any shape can betaken, so long as the shape can ensure efficient hydrogen storing or canbe readily applied as an electrode.

The present invention will be explained in detail below, referring tothe drawings.

EXAMPLE 1

In this Example, a rod-shaped hydrogen storing member in a three-layerstructure comprising a pair of first hydrogen storing materials and asecond hydrogen storing material being provided between the firsthydrogen storing materials was used to occlude deuterium therein byelectrolysis.

FIG. 1 is a schematic cross-sectional view showing one embodiment of arod-like, hydrogen (deuterium) storing member according to the presentinvention, where numeral 1 is a metal as a first hydrogen storingmaterial, such as Pd, etc. and 2 is a second hydrogen storing materialcovering the first hydrogen storing material 1, and a hydrogen storingalloy, etc. capable of shifting into the α phase with a temperaturerange where the first hydrogen storing material 1 is in the β phase canbe used as the second hydrogen storing material. Numeral 3 is the firsthydrogen storing material further covering the second hydrogen storingmaterial.

EXAMPLE 1-1

The hydrogen storing member shown in FIG. 1 was prepared in thefollowing manner.

On a rod-like matrix of Pd (4 mm in diameter and 40 mm long)corresponding to numeral 1 in FIG. 1 was formed a thin film of LaNi₅(thickness: about 10 μm) as a deuterium storing alloy corresponding tonumeral 2 in FIG. 1 by plasma melt injection. Then, Pd was vapordeposited thereon in vacuum by resistance heating to form a portion(thickness: 1 μm) corresponding to numeral 3 in FIG. 3, therebyobtaining a hydrogen storing member for storing deuterium.

The thus prepared hydrogen storing member was placed in an apparatusshown in FIG. 4, where numeral 4 is a temperature-controllablethermostat tank, 5 is a heavy water solution containing 0.1 mol / dm² ofLiOD, 6 is a platinum wire anode, 0.5 mm in diameter, 7 is the hydrogenstoring member as a cathode, 8 is a power source.

Heavy water was electrolyzed at an applied voltage of 5 V in theapparatus by repeating one electrolysis step at an electrolytic solutiontemperature of 5° C. for about 30 minutes and another electrolysis stepat an electrolytic solution temperature of 30° C. for about 20 minutesfor total duration of about 10 days. The solution temperature wascontrolled by controlling the temperature of the thermostat tank 4through a control means (not shown in the drawing).

In this process, Pd corresponding to the first hydrogen storingmaterials 1 and 3 and LaNi₅ corresponding to the second hydrogen storingmaterial 2 occluded deuterium at an electrolytic solution temperature of5° C., and then at an elevated temperature of 30° C., Pd of the members1 and 3 was kept in the β phase, whereas LaNi₅ of the member 2 wasshifted into the α phase. That is, the deuterium was released from theLaNi₅ layer, and the deuterium released at a high density could beconfined into the Pd layers at a high concentration.

In order to occasion cold nuclear fusion reaction, deuterium must beconfined at a high density so that the atomic nuclei themselves canfrequently collide one another. According to the above-mentioned S. E.Jones et al report, it could be confirmed that the nuclear fusionreaction took place by the measurement of neutrons and γ-rays.

In this example, a liquid scintilator was provided around the apparatusto measure the γ-rays by a scintilation counter during the electrolysison the 10th day, and it was found that 3-fold emission of γ-rays wasdetected against the background.

COMPARATIVE EXAMPLE 1-1

When simple Pd was used as the cathode in the same process as in Example1-1, only emission of γ-rays substantially on the same level as that ofthe background was detected.

EXAMPLE 1-2

On a Pd rod corresponding to the member 1 in FIG. 1 was formed FeTi asthe second hydrogen storing material corresponding to the member 2 byplasma melt injection, and then Pd3 was vapor deposited on the FeTi inthe same manner as in Example 1-1, thereby preparing a hydrogen storingmember for storing deuterium. Then, the thus prepared hydrogen storingmember was electrolyzed in the same process as in Example 1-1. The sameresult as in Example 1-1 was obtained.

EXAMPLE 1-3

On a Ti rod as a first hydrogen storing material corresponding to themember 1 in FIG. 1 was formed LaNi₅ as a second hydrogen storingmaterial corresponding to the member 2 by plasma melt injection, and Tiwas further vapor deposited on the LaNi₅ in the same manner as inExample 1-1, thereby preparing a hydrogen storing member. Then, the thusobtained hydrogen storing member was electrolyzed in the same processesin Example 1. The same result as in Example 1-1 was obtained.

In the foregoing examples, the shape of the hydrogen storing member forstoring deuterium was a cylindrical (rod) form, but any appropriateshape such as a spherical form, a thin film form, etc. can be used.Particularly in case of spherical shape, a uniform pressure can beapplied to the spherical hydrogen storing member during the storage ofdeuterium, and thus a better effect can be obtained.

EXAMPLE 2

Storage of deuterium into the hydrogen storing member can be alsocarried out in the following manner besides the electrolysis process.That is, the process used in this example is to store deuterium bybringing a vessel containing the hydrogen storing member into adeuterium gas atmosphere compressed to a pressure of a few to a few tensof atmospheres and utilizing a solid solution equilibrium state of ametal hydride composed of two elements, i.e. a metal and deuterium,under a high pressure.

EXAMPLE 2-1

A hydrogen storing member 12 having the same structure and dimension asthat used in Example 1-1 was used in an apparatus shown in FIG. 5, wherenumeral 9 is a deuterium gas bomb, 11 is a high pressure pipe ofstainless steel, etc. (e.g. 10 mm in outer diameter, 6 mm in innerdiameter and 400 mm long), 10 and 14 are valves provided in a pipingconnecting the gas bomb 9 to the high pressure pipe 11, and 13 is a ventline connected to the piping between the valves 10 and 14 on one handand also connected to a vacuum pump 16 on the other hand.

At first, the hydrogen storing member 12 was placed in the high pressurepipe 11, and the inside of high pressure pipe 11 was brought into avacuum state by evacuation through the vent line 13, while keeping onlythe valve 10 in an open state. This was to remove light hydrogen tofacilitate storing of only deuterium into the hydrogen storing member12.

Then, the vent line 13 was closed and the valve 14 was brought into anopen state to lead deuterium from the bomb 9 into the high pressure pipe11. The valve 10 was closed when the pressure reached about 10 atm (23°C.) in the high pressure pipe 11. The high pressure pipe 11 wassubjected repeatedly to cycles each of cooling the high pressure pipe 11to 5° C. and elevating the pipe 11 to 50° C. in that state for one cycletime of about 5 minutes. That is, in this embodiment, cycles of bothtemperature and pressure were applied.

Approximately on the 7th day γ-rays were measured. About 2-fold emissionof γ-rays was detected against the background.

COMPARATIVE EXAMPLE 2-1

The same process as that of Example 2-1 was carried out for simple Pd.Only emission of γ-rays on the same level as that of the background wasdetected.

EXAMPLE 3

The foregoing Examples 1 and 2 relate to storing of deuterium. Thepresent invention is also very effective as a light hydrogen storingmember. Its embodiment will be given below.

EXAMPLE 3-1

Electrolysis was carried out in the same manner as in Example 1-1 forabout 3 days, using the same hydrogen storing member as in Example 1-1.Then, the hydrogen storing metallic member was broken to take out onlyPd from the inside. The hydrogen content of the thus obtained Pd wasmeasured by thermogravimetric analysis. It was found that the hydrogenwas stored at such a high concentration as Pd:H=1:0.8.

COMPARATIVE EXAMPLE 3-1

When simple Pd was used in the same process as in Example 3-1, thehydrogen was stored at such a concentration as Pd:H=1:0.4

EXAMPLE 4

The hydrogen storing members used in the foregoing Examples were in ablock form having some sizes such as a rod, etc. A hydrogen storingmember, when constituted by providing a second hydrogen storing materialbetween first hydrogen storing materials, may be not in such a blockform, for example, may be in a powdery or fine particulate state.

FIG. 6 shows a structure of a hydrogen storing member constituted bysuch powdery (particulate) hydrogen storing materials, where numeral 1ais Pd powder as a first hydrogen storing material serving as a matrix,2a is LaNi₅ powder as a second hydrogen storing material, formedthereon, and 3a is Pd powder as the first hydrogen storing material,further formed thereon.

EXAMPLE 4-1

Powdery hydrogen storing member shown in FIG. 6 was prepared in thefollowing manner.

Powdery Pd (average particle size: about 10 μm) was dipped in adispersion of LaNi₅ hydrogen storing alloy powder inpolytetrafluoroethylene (PTFE) and then taken out. Then, the taken outpowder was coated with a solution of organic polymer binder such aspolyethylene, polytetrafluoroethylene, etc., and heat treated in aninert gas atmosphere to scatter the solvent, thereby obtaining thepowder constituted by the members 1a and 2a. Then, the powder was dippedin an organic palladium solution (i.e. CCP-4230, trademark of a productmade by Okuno Seiyaku K. K., Japan), taken out, heated at 250° C. for 10minutes to scatter the binder of organic palladium, and thenheat-treated in a reducing atmosphere at 300° C.

The thus prepared powdery hydrogen storing member was subjected totemperature cycles in a hydrogen atmosphere under 1 atm for about onehour in the same manner as in Example 1-1, and then the composition wasanalyzed. It was found that hydrogen was stored at a higherconcentration such as Pd:H=1:0.9 (atomic ratio).

COMPARATIVE EXAMPLE 4-1

Powder of only Pd was subjected to hydrogen storage in the same manneras in Example 4-1. It was found that the concentration was Pd:H=1:0.5(atomic ratio).

In the foregoing examples, temperature cycles or temperature-pressurecycles were applied to the hydrogen storing members, but the hydrogenstorage can be also carried out only by pressure cycles.

As explained above, hydrogen can be stored into a hydrogen storingmember efficiently at a high concentration in the present invention byconstituting the hydrogen storing member from a first hydrogen storingmaterial and a second hydrogen storing material capable of shiftingphases (α←→β) while keeping the first hydrogen storing material in astable region for the single B phase having a high capacity for storinghydrogen and by conducting storing or release of hydrogen into or fromthe second hydrogen storing material in a hydrogen atmosphere, therebypumping much more hydrogen into the first hydrogen storing material.When the present invention is applied to deuterium, a probability ofnuclear fusion can be enhanced.

We claim:
 1. A process for preparing a deuterium storing membercontaining deuterium, which comprises:(a) disposing a deuterium storingmember in a temperature-controllable vessel, wherein the deuteriumstoring member comprises a thick first deuterium storing material membergenerating β phase which is capable of storing deuterium at a firsttemperature range and generating β phase which is capable of storingdeuterium at a second temperature range set at a lower temperature thanthe first temperature range, a thin film of a second deuterium storingmaterial provided on the thick first deuterium storing material membergenerating α phase which is capable of releasing deuterium at the firsttemperature range and generating β phase which is capable of storingdeuterium at the second temperature range set at a lower temperaturethan the first temperature range, and a thin film of said firstdeuterium storing material provided on the thin film of the seconddeuterium storing material generating β phase which is capable ofstoring deuterium at the first temperature range and generating β phasewhich is capable of storing deuterium at the second temperature rangeset at a lower temperature than the first temperature range; (b) settingthe vessel at a temperature within the second temperature range andproviding the inside of the vessel with a high pressure deuterium gasatmosphere; and (c) setting the vessel at a temperature within the firsttemperature range and providing the inside of the vessel with a highpressure deuterium gas atmosphere.
 2. The process according to claim 1,wherein the deuterium is introduced after light hydrogen is removed fromthe vessel under vacuum.